Process for defouling equipment contaminated with carbonaceous deposits



3,420,711 TED Jan. 7, 1969 R. P. VAN DRIESEN PROCESS FOR DEFOULINGEQUIPMENT CONTAMINA WITH. CARBONACEOUS DEPOSITS Filed April 26, 1966PRIMARY & ANCILLARY EQUIPMENT INVENTOR ROGER P. VAN DRI MM SEN ATTORNEYUnited States Patent 7 Claims The present invention relates to a processfor defouling process equipment. More particularly, the inventionprovides an effective method for defouling process equipmentcontaminated with combustible carbonaceous deposits.

The equipment utilized in many types of chemical processes becomesfouled from time to time by the formation of combustible carbonaceouscontaminants. Exemplary of equipment susceptible to fouling by theformation of carbonaceous contaminants are thermal cracking units,hydrocracking units, polymerization units, etc. A number of procedureshave heretofore been used to clean up fouled equipment. Thus, thecarbonaceous materials may be burned with steam diluted with air orsubjected to chemical washing. These procedures have not been entirelysatisfactory or practical in many cases. For example, combustion ofcarbonaceous contaminants in hydrocracking units with steam diluted withair often requires unit shutdown times on the order of days or weeks.Extended shutdown periods of this order cannot, of course, be toleratedfrom an economic standpoint.

In accordance with my present invention, an improved process is providedfor defouling equipment of combustible carbonaceous contaminants. Moreparticularly, the invention enables relatively rapid combustion ofcarbonaceous contaminants contained in process equipment. Various otherobjects and advantages of the invention will become apparent from thefollowing detailed description thereof.

Briefly, the defouling process contemplated by the invention comprisescontacting the fouled surfaces of the equipment with an admixture of anoxygen-containing gas and water at an elevated temperature andsuperatmospheric pressure sufiicient to maintain at least a portion ofthe water in the liquid phase. Under these conditions, the carbonaceousdeposits are rapidly combusted and the heat of combustion is absorbed bythe liquid water. The absorption by the water of the heat given off inthe combustion avoids excessive temperature increase, and accordinglyrenders the present invention practical in defouling equipment notcapable of withstanding the relatively high temperature attendant priorart steam-air defouling operations.

As just noted, it is a prime requirement of the inven tion that thetemperature and pressure conditions at which the contacting with thecarbonaceous contaminants within the equipment to be defouled is carriedout are such to maintain liquid phase water in contact with the fouledequipment. For this purpose, the temperature of the oxygen containinggas-water mixture introduced into the equipment to be defouled is suchthat upon combustion of the carbonaceous contaminants, the temperatureis not increased to above about 700 F. (approximately the criticaltemperature of water) by absorption of the heat given off in thecombustion reaction. It will, of course, be appreciated that the extentor rate of combustion will be primarily determined by the maximumtemperature reached in the contacting ope-ration. Thus, at contactingtemperatures below about 400 F., excessively long periods of time arerequired for defouling the equipment. Accordingly, the contactingtemperature may, with advantage, range from about 400 F. to about 700 F.with the range of 500 F. to about 650 F. being particularly desirable.The pressure at which the defouling operation of the invention iscarried out is high enough to maintain at least some liquid phase waterin contact with the fouled equipment at the operating temperature.Advantageously, the pressure is maintained within the range of fromabout 300 p.s.i.g. to about 5,000 p.s.i.g. particularly from about 700p.s.i.g. to about 4,000 ps.i.g.

The oxygen-containing gas useful in the present process may be any gascontaining molecular oxygen, such as oxygen itself, air oroxygen-enriched air. Air is preferred.

In carrying out the present process, I prefer to maintain substantiallyall of the fouled equipment in contact with a continuous phase of liquidwater having the oxygencontaining gas dissolved or dispersed therein.The oxygencontaining gas may preferably be passed through the fouledequipment at rates which result in at least a 50 volume percentinventory of liquid water in the fouled equipment. For this purpose, theoxygen-containing gas may be passed through the equipment at ratesranging from about 0.03 to about 0.5 ft. /sec. per square foot ofequipment cross-section, preferably from about 0.05 to about 0.3 ft./sec. per ft. of cross-section.

Various suitable methods may be employed for maintaining the fouledequipment in substantially complete contact with a continuous phase ofliquid water with the oxygen-containing gas dissolved or dispersedtherein during combustion of the carbonaceous deposits, in accordancewith the preferred embodiment of the invention. By way of illustration,one suitable process scheme which may be employed is diagrammaticallyrepresented in the attached drawing.

Referring to the drawing, reference numeral 1 represents equipment to bedefouled of combustible carbonaceous solids. Equipment 1 may, forexample, be a reactor or ancillary apparatus employed in hydrocracking,thermal cracking, polymerization or like high pressure processes, whichbecomes fouled from time to time by the formation of combustiblecarbonaceous byproducts. When the buildup of carbonaceous solidsseriously hampers the operation of the process, the supply of feed tothe equipment is terminated and the equipment is then generally purgedof residual liquid or vaporous material.

Defouling of equipment 1 is accomplished in accordance with a preferredembodiment of the present invention by introducing water having anoxygen-containing gas, such as air, substantially completely dissolvedtherein through inlet 2. The solution of oxygen-containing gas in waterpassed through the equipment under suitable conditions of pressure andtemperature, as noted above, to maintain the water substantially solelyin the liquid phase in contact with the fouled equipment, and to combustthe carbonaceous contaminants.

The oxygen-lean solution is passed from the equipment 1 through line 3and is introduced into an absorption tower 4. Air is supplied to theabsorption tower 4 through line 5 and compressor 6 and is absorbed inthe oxygen-lean water. Absorption efiiciency is enhanced by allowing thewater to descend through packing bodies 7 supported on a grid 8. Thepacking bodies are those conventionally used in absorbing towers,including Raschig rings, Berl saddles and the like. Gaseous products ofthe combustion of the carbonaceous contaminants, e.g., CO and CO arepartially stripped from the water, and along with steam and any excessoxygen-containing gas are vented from the absorbing tower through line9. The water level in the absorbing tower may be maintained as desiredby liquid level controller 10 which controls the operation of valve 11in excess water drawoif line 12.

In order to maintain suitable pressure conditions for the defouling ofequipment 1, absorber 4 is suitably maintained under a total pressure offrom about 300 to about 5,000 p.s.i.g. and preferably 700 to 4,000p.s.i.g., the oxygen partial pressure being at least about 10 p.s.i.,preferably 100 to 500 p.s.i. Furthermore, the temperature within theabsorber 4 is preferably such that the vapor pressure of water is lessthan about 80% of the operating pressure. This practice minimizes theventing of large quantities of steam from the absorber through line 9.

The oxygen-rich water is passed from the absorption tower through line13 and mixed in line 2 with make-up water charged through line 14. Theamount and temperature of makeup water added through line 14 are suchthat there is no substantial vapor buildup in equipment 1 due to gassingoff as the temperature is increased by the heat of combustion. Aspreviously noted, by maintaining the air-Water solution substantiallysolely in the liquid phase, possible dangers of explosion or damage toequipment 1 due to extremely rapid combustion occurring in vapor buildupareas are eliminated.

The time required for defouling the equipment is, of course, a functionof the amount of carbonaceous contaminants contained therein as well asthe temperature, total pressure and partial pressure and oxygenconcentration, and may be readily determined by those skilled in the artas noted above. Compared to prior art processes employing steam dilutedwith air, defouling may be accomplished far more readily in accordancewith the present invention.

The following specific examples are included for the purpose of furtherillustrating the invention, but are not intended to limit the inventionthereto.

EXAMPLE 1 Using the procedure and apparatus arrangement described inreference to the drawing, a hydrogenation unit containing an estimated800 pounds of combustible carbonaceous contaminants is defouled. Air, atthe rate of 60,- 750 s.c.f.h. is added to an absorption tower, andtherein is absorbed in oxygen-lean water passed from the hydrogenationunit being defouled. The absorption tower is operated at a temperatureof 600 F. and a pressure of 3,000 p.s.i.g., which are essentially thetemperature and pressure conditions at which the defouling of thehydrogenation unit is conducted. Oxygen partial pressure isapproximately 310 p.s.i.

Water having air dissolved therein in the amount of 0.01 mole of pergallon of water, is passed from the bottom of the absorption tower at arate of 18,700 gallons per hour and is combined with 246 F. make-upwater added at the rate of 17,000 pounds per hour. The resultantadmixture, which has a temperature of 581 F., is passed to thehydrogenation unit.

This procedure is continued for four (4) hours at which time thehydrogenation unit is ascertained to be completely defouled.

EXAMPLE 2 This example illustrates the use of the present invention indefouling a hydrocracking unit comprising a coil in which oil andhydrogen are reacted at high temperature and pressure. Coke and highmolecular weight carbonaceous contaminants periodically buildup in thecoil, thereby hampering efiicient operation of the hydrocrackingprocess. Heretofore, normal defouling procedure involved passing steamdiluted with air through the coil. It was necessary to maintain the airconcentration at a low level in order to prevent overheating and coildamage. However, on occasion, the coil was damaged by the excessivetemperature attendant this type of defouling operation, requiringreplacement of at least one coil section. Furthermore, down-streamequipment such as heat exchangers and the like could not withstand thehigh temperatures required for combustion on the carbonaceouscontaminants (over 1,000 F.). Consequently, the downstream equipment hadto be dismantled and manually cleaned at considerable time and expense,The Whole operation required a minimum of four (4) to five (5) days andoften much longer.

In accordance with the present invention, the following defoulingoperation is completed in twelve (12) hours without dismantling ordamaging the equipment:

The hydrocracking operation is discontinued and the unit is cooled fromoperating temperature of 850 F. to about 600 F. During the coolingperiod, the normal heavy oil feedstock is discontinued in favor of alighter, more volatile oil. After a two (2) hour wash with this oil, theoil feed is discontinued. Circulation of hydrogen at 600 F. vaporizesthe oil in two (2) additional hours. The unit is then depressured andpurged with flue gas, this operation requiring one 1) hour.

The defouling operation is conducted by maintaining the hydrocrackingcoil substantially completely in contact with a continuous phase liquidwater having air dispersed therein. More particularly, water at the rateof 20,000 pounds per hour and air at the rate of 60,250 s.c.f.h. arecontinuously admixed and pumped through the coil. The temperature at theinlet is 524 F while the temperature at the outlet is 26 higher (i.e.550 F.) due to the heat given off by combustion of the carbonaceousdeposits. Total operating pressure is 1500 p.s.i.g., and oxygen partialpressure is p.s.i. After an operating period of about three (3) hours,the reaction temperature falls off to the inlet condition of 524 F.,indicating that the bulk of the carbonaceous deposits has beencombusted. The defouling operation is terminated after one (1) hour ofoperation, and the unit is then purged with flue gas for one (1) hour.

Hydrogen and oil feed to the unit are then resumed, and within two (2)hours the unit is again on-stream. The hydrocracking operation proceedssmoothly indicating that the carbonaceous contaminants are substantiallycompletely combusted.

While the invention has been described above in connection with certainpreferred embodiments thereof, it will be understood by those skilled inthe art that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention as expressed in theappended claims.

Therefore, I claim:

1. Process for defouling process equipment of combustible carbonaceousdeposits which comprises contacting the surfaces of the processequipment fouled with carbonaceous deposits with an admixture of waterand an oxygen-containing gas at an elevated temperature to combust thecarbonaceous deposits and at a superatmospheric pressure sufiicient tomaintain the fouled surfaces of the equipment in substantially completecontact with a continuous phase of liquid water with theoxygen-containing gas dispersed therein during combustion of thecarbonaceous deposits, the heat of combustion being at least partiallyabsorbed by the liquid Water.

2. Process as in claim 1 wherein the oxygen-containing gas and water arecontacted with said fouled surfaces at a temperature of from about 400F. to about 700 F. and a pressure of from about 300 p.s.i.g. to about5,000 P.S.l.g.

3. Process as in claim 2 wherein the temperature is within the range offrom about 500 F. to about 650 F. and the pressure is within the rangeof from about 700 p.s.i.g. to about 4,000 p.s.i.g.

4. Process as in claim 1 wherein substantially all of the surfaces ofthe fouled equipment are maintained in contact with a continuous phaseof water in admixture with oxygen-containing gas.

5. Process as in claim 4 wherein the oxygen-containing gas iscontinuously passed through the fouled equipment at a rate which resultsin at least a 50 volume percent inventory of liquid water in the fouledequipment.

6. Process as in claim 1 wherein the oxygen-containing gas issubstantially completely dissolved in the water and wherein thecontinuous phase of liquid water occupies substantially the entirevolume of the fouled equipment.

5 6 7. Process as in claim 1 wherein the oxygen-containing 2,563,0858/1951 Utsinger l342 gas is air. 2,577,254 12/ 195 1 Lawson l342References Cited UNITED STATES PATENTS MORRIS O. WOLIF, PrzmaryAfTxammer. 1,470,359 10/1923 Greenstreet 134-22 5 ZATARGA Ammm Examine-2,289,35O 7/1942 Dixon et a1 134-20 US. Cl. X.R.

2,423,157 7/1947 Reiss 13420, 22, 39

1. PROCESS FOR DEFOULING PROCESS EQUIPMENT OF COMBUSTIBLE CARBONACEOUSDEPOSITS WHICH COMPRISE CONTACTING THE SURFACES OF THE PROCESS EQUIPMENTFOULED WITH CARBONACEOUS DEPOSITS WITH AN ADMIXTURE OF WATER AND ANOXYGEN-CONTAINING GAS AT AN ELEVATED TEMPERATURE TO COMBUST THECARBONACEOUS DEPOSITS AND AT A SUPERATMOSPHERIC PRESSURE SUFFICIENT TOMAINTAIN THE FOULED SURFACES OF THE EQUIPMENT IN SUBSTANTIALLY COMPLETECONTACT WITH A CONTINUOUS PHASE OF LIQUID WATER WITH THE OXYGEN-CONTAINING GAS DISPERSED THEREIN DURING COMBUSTION OF THE